I understand the meaning, and to be sure I searched its definition: something that requires or involves little or no mental effort. This noun literally can have another meaning logically to describe a person, it makes sense to me. My question is, is it the right usage to use no-brainer to describe someone who don't use their brain to think at all?

An appropriate term for what you are wanting to describe might be 'empty-headed'
– DaveMongooseDec 17 '18 at 12:04

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This isn't the question you asked, which has been ably answered multiple times below, but some terms which you could use for a person who is not using the brain are halfwit, dimwit, ignoramus, dunce, dunderhead, numskull, shit-for-brains, ... (I can't believe how easily that list came to me).
– cobaltduckDec 17 '18 at 12:15

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If I heard you say that "Person X is a no-brainer" I would first think that you had to select a person to fill a position and Person X was far and away the best person for that role
– Stephen SDec 17 '18 at 15:26

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@DaveMongoose aren't you amazed at English language that empty-headed and no-brainer literally mean the same thing but you use them so differently.
– drerDDec 17 '18 at 19:16

@drerD I think you have similar cases in other languages as well, but English certainly has a lot of them!
– DaveMongooseDec 18 '18 at 12:12

5 Answers
5

Yes.

Something that requires or involves little mental effort or intelligence to perform or understand; esp. an easily made decision

But it also includes the definition you mention:

A foolish or unintelligent person or action.

They quote the sentence: "If a no-brainer wants to talk on the radio—even if the message makes no sense whatsoever—he or she can do it."

But...

It's worth noting that as a native English speaker, I wasn't familiar with this definition (and neither it seems, were the other answerers), so while it does exist, I would advise against using it unless you hear it often in your region.

Although it's possible (but admittedly rare) that you might use metonymy to refer to a decision involving a person as that person. E.g.: "We should try to predict which of these students are likely to pass this class." "Well, Sally's a no-brainer." This would mean that Sally is either so bad or so good at the subject that it's obvious ahead of time whether or not she's likely to pass. Trying to guess whether she'll pass or not is very easy, i.e. a no-brainer.
– Admiral JotaDec 17 '18 at 16:15

You could, and in context people will understand the intended meaning, but at the same time people will be aware that you are using the term wrong. A "no-brainer" already has a different definition: it refers to a problem, a task, or a decision.

You can use your meaning in the context of sarcasm, jokes, or if you're intentionally trying to show unfamiliarity with the language.